U.S. patent number 8,062,614 [Application Number 12/870,183] was granted by the patent office on 2011-11-22 for methods for improving the recovery of metal leaching agents.
This patent grant is currently assigned to Cognis IP Management GmbH. Invention is credited to Gary A. Kordosky, Andrew Nisbett.
United States Patent |
8,062,614 |
Kordosky , et al. |
November 22, 2011 |
Methods for improving the recovery of metal leaching agents
Abstract
Processes for metal leaching/solvent extraction are described
which comprise: (a) providing a first aqueous leach pulp which
comprises a mixture of leached solids and an aqueous leach solution
comprising a metal, a leaching agent and water; (b) subjecting the
first aqueous leach pulp to a first solid-liquid separation to
provide a first clarified aqueous leach solution and a second
aqueous leach pulp, wherein the second aqueous leach pulp comprises
the leached solids at a % solids level greater than the first pulp;
(c) subjecting the first clarified aqueous leach solution to a
first solvent extraction prior to any significant dilution, whereby
a first aqueous raffinate is obtained; (d) subjecting the second
aqueous leach pulp to a second solid-liquid separation with
dilution via an aqueous stream to obtain a second clarified aqueous
leach solution; and (e) subjecting the second clarified aqueous
leach solution to a second solvent extraction whereby a second is
aqueous raffinate is obtained.
Inventors: |
Kordosky; Gary A. (Tucson,
AZ), Nisbett; Andrew (Tucson, AZ) |
Assignee: |
Cognis IP Management GmbH
(Duesseldorf, DE)
|
Family
ID: |
34118858 |
Appl.
No.: |
12/870,183 |
Filed: |
August 27, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100319490 A1 |
Dec 23, 2010 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10895794 |
Jul 21, 2004 |
7799294 |
|
|
|
60491311 |
Jul 30, 2003 |
|
|
|
|
Current U.S.
Class: |
423/24; 205/581;
423/32; 423/99; 205/607; 205/590; 75/722; 205/604; 205/580;
205/608; 423/109; 423/139; 423/33; 75/743; 423/150.1; 205/583;
205/589; 205/606; 205/582; 205/605; 205/591 |
Current CPC
Class: |
C22B
15/0071 (20130101); C22B 15/0084 (20130101); C22B
15/0065 (20130101); C22B 3/26 (20210501); Y02P
10/20 (20151101) |
Current International
Class: |
C22B
23/00 (20060101) |
Field of
Search: |
;423/24,32,33,99,109,139,150.1 ;205/580-583,589-591,604-608
;75/722,743 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Zinc Solvent Extraction in the Process Industries", P.M. Cole and
K.C. Sole, Mineral Processing & Extractive Metallurgy Reviews,
24, 91-137, 2003. cited by other .
"Ammoniacal Solvent Extraction Process at Queensland Nickel,
Process Installation and Operation", J.G. Reid and M.J. Price,
Solvent Extraction in the Process Industries, vol. 1, pp. 225-231,
Proceedings of ISEX '93, Ed. D. H. Logsdail and M.J. Slater,
published for SCI by Elsevier Applied Science, London and New York.
cited by other .
"Cominco's Trail zinc pressure leach operation", M. T. Martin CIM
Bulletin, Apr. 1985 Extractive Metallurgy, pp. 77-81. cited by
other .
"The recovery of nickel from high-pressure acid leach solutions
using mixed hydroxide product--LIX.RTM. 84-INS Technology", M.
Mackenzie et al. pp. 1-23. cited by other .
"Ammonia leaching process for Escondida copper concentrates".
W.P.C. Duyvesteyn and B.J. Sabacky, Extractive metallurgy of
copper, nickel and cobalt, vol. 1., 1993, pp. C125-C140. cited by
other .
"Hydrometallurgy, Research, Development and Plant Practice" W.
Hopkins et al., Mar. 1983; pp. 984-999. cited by other .
"The Development of a Novel Hydrometallurgical Process for Nickel
and Cobalt Recovery from Goro Laterite Ore"I. Mihaylov et al., CIM
Bulletin, 93 (1041), 2000, pp. 124-120; (pp. 1-11). cited by other
.
"Roast additives are key in UOP nickel process", Donald A. Pazour,
World Mining, Jul. 1979; 5 pages. cited by other .
"New recovery process can yield both electrolytic nickel and
copper" reprinted from Engineering and Mining Journal, 2 pages.
cited by other .
Case Studies B "Ammoniacal Pressure Leaching" R. Berezowsky, pp.
4-13 to 4-31. cited by other .
Official Opening if the Tailings Leach Plant Stage III Nchanga
Division, Zambia Consolidated Copper Mines Limited Brochure, Sep.
25, 1986, pp. 1-12. cited by other .
Hopkins, et al. "Anamax Oxide Plant: A New US Dimension In Solvent
Extraction", Reprinted from Engineering & Mining Journal,
McGraw Hill, Inc., Feb. 1977, pp. 1-9. cited by other .
W.P.C. Duyvesteyn & B.J. Sabacky, "The Escondida Process for
Copper Concentrates" The Minerals Laboratory; The Minerals, Metals
& Materials Society; 1993; pp. 881-910. cited by other .
King, et al., "Autoclaving of Copper Concentrates"; Proceedings of
COPPER 95-COBRE Int'l. Conf., vol. III, 1995; pp. 511-533. cited by
other .
Bartlett, R.W., "Solution Mining: Leaching and Fluid Recovery of
Materials," Gordon and Breach Publishers; 1992; cover page, inside
page, and pp. 80-81. cited by other.
|
Primary Examiner: Bos; Steven
Attorney, Agent or Firm: Diehl Servilla LLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No.
10/895,794, filed Jul. 21, 2004, which claims priority, under 35
U.S.C. .sctn.119(e), of U.S. Provisional Patent Application No.
60/491,311, filed on Jul. 30, 2003, the entire contents of which
are hereby incorporated by reference.
Claims
What is claimed is:
1. A process comprising: (a) providing a first aqueous leach pulp
which comprises a mixture of leached solids and an aqueous leach
solution comprising ammonia, water, and one or more metals selected
from the group consisting of copper, zinc, cobalt, and nickel; (b)
subjecting the first aqueous leach pulp to a first solid-liquid
separation to provide a first clarified aqueous leach solution and
a second aqueous leach pulp, wherein the second aqueous leach pulp
comprises the leached solids at a % solids level greater than the
first pulp; (c) subjecting the first clarified aqueous leach
solution to a first solvent extraction prior to any significant
dilution, to obtain a first aqueous raffinate; (d) subjecting the
second aqueous leach pulp to a second solid-liquid separation with
significant dilution via an aqueous stream to obtain a second
clarified aqueous leach solution; and (e) subjecting the second
clarified aqueous leach solution to a second solvent extraction to
obtain a second aqueous raffinate.
2. The process according to claim 1, wherein the volume of the
aqueous leach solution in the first clarified aqueous leach
solution is greater than the volume of the aqueous leach solution
in the second aqueous leach pulp.
3. The process according to claim 1, wherein the aqueous stream for
diluting the second aqueous leach pulp comprises the second aqueous
raffinate.
4. The process according to claim 3, wherein the aqueous stream
comprising the second aqueous raffinate is at least partly
neutralized prior to dilution of the second aqueous leach pulp.
5. The process according to claim 1, wherein the second aqueous
leach pulp is subjected to the second solid-liquid separation prior
to dilution.
6. The process according to claim 1, wherein the second aqueous
leach pulp is subjected to the second solid-liquid separation
simultaneously with dilution.
7. The process according to claim 6, wherein the second
solid-liquid separation comprises counter-current decantation.
8. The process according to claim 1, wherein the concentration of
the metal in the first clarified aqueous leach solution is at least
10% greater than the concentration of the metal in the second
clarified aqueous leach solution.
9. The process according to claim 1, wherein the concentration of
the metal in the first clarified aqueous leach solution is at least
50% greater than the concentration of the metal in the second
clarified aqueous leach solution.
10. The process according to claim 1, wherein the concentration of
the metal in the first clarified aqueous leach solution is at least
100% greater than the concentration of the metal in the second
clarified aqueous leach solution.
11. The process according to claim 1, wherein at least a portion of
the first aqueous raffinate is recycled to a leaching process.
12. The process according to claim 1, wherein the first aqueous
leach pulp is obtained from a leaching process and wherein at least
a portion of the first aqueous raffinate is recycled to the
leaching process.
13. The process according to claim 1, wherein at least a portion of
the second aqueous raffinate is recycled to a leaching process.
14. The process according to claim 1, wherein the first aqueous
leach pulp is obtained from a leaching process and wherein at least
a portion of the second aqueous raffinate is recycled to the
leaching process.
15. The process according to claim 1, wherein the first aqueous
leach pulp is obtained from a leaching process and wherein at least
a portion of the first aqueous raffinate and at least a portion of
the second aqueous raffinate are recycled to the leaching
process.
16. A process comprising: (a) providing a first aqueous leach pulp,
wherein the first aqueous leach pulp comprises a mixture of leached
solids and an aqueous leach solution comprising ammonia, water, and
one or more metals selected from the group consisting of copper,
zinc, cobalt, and nickel; (b) subjecting the first aqueous leach
pulp to a first solid-liquid separation to provide a first
clarified aqueous leach solution and a second aqueous leach pulp,
wherein the second aqueous leach pulp comprises the leached solids
at a % solids level greater than the first pulp; (c) subjecting the
first clarified aqueous leach solution to a first solvent
extraction prior to any significant dilution, to obtain a first
aqueous raffinate; (d) subjecting the second aqueous leach pulp to
a second solid-liquid separation with significant dilution via an
aqueous stream to obtain a second clarified aqueous leach solution,
wherein the concentration of the metal in the first clarified
aqueous leach solution is at least 10% greater than the
concentration of the metal in the second clarified aqueous leach
solution; (e) subjecting the second clarified aqueous leach
solution to a second solvent extraction to obtain a second aqueous
raffinate; wherein the aqueous stream for diluting the second
aqueous leach pulp comprises at least a portion of the second
aqueous raffinate; and (f) recycling at least a portion of the
first aqueous raffinate and at least a portion of the second
aqueous raffinate to a leaching process.
17. The process according to claim 16, wherein the concentration of
the metal in the first clarified aqueous leach solution is at least
50% greater than the concentration of the metal in the second
clarified aqueous leach solution.
18. The process according to claim 16, wherein the concentration of
the metal in the first clarified aqueous leach solution is at least
100% greater than the concentration of the metal in the second
clarified aqueous leach solution.
Description
BACKGROUND OF THE INVENTION
Most metals are obtained by removing those metal values from the
ores in which they are found in the ground. Once the ore has been
mined, the metal must then be separated from the remainder of the
ore. One method to separate the metal from the ore is known as
leaching. In general, the first step in this process is contacting
the mined ore with an aqueous is solution containing a leaching
agent which extracts the metal from the ore into solution. For
example, in copper leaching operations, such as, for example, in
the agitation leaching of copper oxide ores, sulfuric acid in an
aqueous solution is contacted with copper oxide minerals. During
the leaching process, acid in the leach solution is consumed and
copper is dissolved thereby increasing the copper content of the
aqueous solution.
The aqueous leach solution containing the leached metal can then be
treated via a known process referred to as solvent extraction
wherein the aqueous leach solution is contacted with a nonaqueous
solution containing a metal-specific extraction reagent. The
metal-specific extraction reagent extracts the metal from the
aqueous phase into the non-aqueous phase. During the solvent
extraction process for copper and certain other metals, the
leaching agent is regenerated in the aqueous phase. In the case
where sulfuric acid is the leaching agent, sulfuric acid is
regenerated in the aqueous phase when copper is extracted into the
organic phase by the extraction reagent. Normally, for every ton of
copper removed from the leach solution about 1.5 tons of sulfuric
acid is generated in the leach solution.
Leaching agents are often recycled back to the leaching process to
dissolve more metal and the more leaching agent that can be
recycled the less that needs to be obtained from another source. In
a standard agitation leaching process for copper, followed by
solvent extraction, the leach solution is diluted to a lesser or
greater extent with water in conjunction with the solid-liquid
separation process needed to provide a clarified leach liquor and
tailings. The diluted clarified leach solution is then transferred
to one or more solvent extraction plants depending on the volume of
leach solution and the capacity of each plant. The diluted leach
solution undergoes solvent extraction wherein copper is removed
from, and the sulfuric acid concentration is increased in, the
aqueous phase. A portion of this copper-depleted, acid-containing
aqueous phase, now called the raffinate, is then recycled back to
the leaching process. The other portion is recycled back to the
front of the solid-liquid separation process where it dilutes the
leach solution exiting the agitation leaching process. Depending on
the acid balance across the whole process some of this recycled
aqueous phase may be partially neutralized.
The leach solution from an agitation leach process is normally
diluted during the solid-liquid separation step in order to
maximize the washing of the leached solids so that metal lost to
the solids is minimized. During solvent extraction as the metal is
extracted, acid concentration builds in the aqueous phase and the
reaction becomes self-limiting in equilibrium. However, because of
the initial dilution to maximize metal recovery from the leached
solids, the amount of acid regenerated is lower in concentration
than it would have been if the leach solution had not been diluted
in the washing of the leached solids. Unfortunately, the lower the
concentration of acid in the recycled raffinate, the more fresh
acid that needs to be added and this increases the cost of the
operation.
Accordingly, there is a need in the art for improved processes for
metal leaching and solvent extraction, wherein the recovery of
leaching agents is improved without negatively affecting metal
recovery.
BRIEF SUMMARY OF THE INVENTION
The present invention relates, in general, to metal leaching
operations and methods of improving the recovery of leaching agents
from solvent extraction operations.
It has been surprisingly discovered that by splitting an aqueous
leach solution into two or more portions and subjecting at least
one portion to solvent extraction prior to any significant dilution
and also subjecting at least one other portion to solvent
extraction after dilution, (also referred to herein as a "split
circuit"), that good, and even optimum, metal extraction can be
achieved while significantly improving the recovery of the leaching
agent.
One embodiment of the present invention includes processes which
comprise: (a) providing a first aqueous leach pulp which comprises
a mixture of leached solids and an aqueous leach solution
comprising a metal, a leaching agent and water; (b) subjecting the
first aqueous leach pulp to a first solid-liquid separation to
provide a first clarified aqueous leach solution and a second
aqueous leach pulp, wherein the second aqueous leach pulp comprises
the leached solids at a % solids level greater than the first pulp;
(c) subjecting the first clarified aqueous leach solution to a
first solvent extraction prior to any significant dilution, whereby
a first aqueous raffinate is obtained; (d) subjecting the second
aqueous leach pulp to a second solid-liquid separation with
significant dilution via an aqueous stream to obtain a second
clarified aqueous leach solution; and (e) subjecting the second
clarified aqueous leach solution to a second solvent extraction
whereby a second aqueous raffinate is obtained.
In many of the preferred embodiments of the present invention, the
metal comprises copper. Also, in many preferred embodiments of the
present invention, the leaching agent comprises sulfuric acid. In
more preferred embodiments of the present invention, the metal
comprises copper and the leaching agent comprises sulfuric
acid.
Another embodiment of the present invention includes processes
which comprise: (a) providing a first aqueous leach pulp obtained
from an agitation leaching process, wherein the first aqueous leach
pulp comprises a mixture of leached solids and an aqueous leach
solution comprising copper, sulfuric acid and water; (b) subjecting
the first aqueous leach pulp to a first solid-liquid separation to
provide a first clarified aqueous leach solution and a second
aqueous leach pulp, wherein the second aqueous leach pulp comprises
the leached solids at a % solids level greater than the first pulp;
(c) subjecting the first clarified aqueous leach solution to a
first solvent extraction prior to any significant dilution, whereby
a first aqueous raffinate is obtained; (d) subjecting the second
aqueous leach pulp to a second solid-liquid separation with
significant dilution via an aqueous stream to obtain a second
clarified aqueous leach solution, wherein the concentration of the
metal in the first clarified aqueous leach solution is greater than
the concentration of the metal in the second clarified aqueous
leach solution; (e) subjecting the diluted second portion to a
second solvent extraction whereby a second aqueous raffinate is
obtained; wherein the aqueous stream for diluting the second
aqueous leach pulp comprises at least a portion of the second
aqueous raffinate; and (f) recycling at least a portion of the
first aqueous raffinate and at least a portion of the second
aqueous raffinate to the leaching process.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a process flow diagram representing a standard
leaching/solvent extraction operation wherein all of the aqueous
leach solution is treated in the same manner.
FIG. 2 is a process flow diagram representing a preferred
embodiment of the present invention wherein an aqueous leach
solution is divided into two portions and subjected to solvent
extraction under two different sets of conditions.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated,
all numbers expressing quantities of ingredients or reaction
conditions used herein are to be understood as modified in all
instances by the term "about".
Aqueous leach pulps from agitation leaching operations comprise a
mixture of leached solids (i.e., ore residues) and an aqueous leach
solution. Aqueous leach solutions comprise water, a leaching agent
and a metal. Aqueous leach solutions can additionally contain other
metals, impurities, and residual leached solids. Aqueous leach
pulps are obtained from the treatment of ground or milled ores with
an aqueous solution of a leaching agent. The aqueous leach pulp
then flows or is carried to further processing and solvent
extraction. The manner in which the aqueous leach pulp, or any
other solution, stream or raffinate is conveyed during the
processes according to the present invention is inconsequential. In
general, pulps, solutions, streams and raffinates may be conveyed
by pipe or any other natural or man-made conduit.
In accordance with the present invention, a first aqueous leach
pulp is subjected to a solid-liquid separation to remove at least
some of the leached solids which are present therein. The first
aqueous leach pulp is divided into two or more portions by
subjecting the aqueous leach pulp to a solid-liquid separation,
such as a decantation-clarifier or filtering, to provide a first
portion or first clarified aqueous leach solution and a second
portion or second aqueous leach pulp, wherein the second pulp
contains leached solids at a higher % solids level than the first
aqueous leach pulp. Essentially, the solid-liquid separation is
used to divide the solution into the two portions for separate
solvent extraction. The first portion is a clarified or partially
clarified leach solution while the second portion is a combination
of leach liquor and leached solids at a higher solids content than
the first aqueous leach pulp. The clarified or partially clarified
leach solution advances to solvent extraction while the second
portion advances to a counter current decantation wash circuit or
to another type of solid-liquid separation that includes some
washing of the solids.
In general, each solid-liquid separation can be carried out in any
known manner. Any method for separating solids from liquids can be
employed. The manner in which solid-liquid extraction is carried
out is not critical. For example, solids can be separated from
liquids by methods including, but not limited to, decantation
and/or filtration. Decantation is preferred.
The processes according to the present invention can be used in any
metal recovery operation which employs an aqueous agitation
leaching operation where the leaching agent is regenerated in the
solvent extraction process. Thus, the processes according to the
present invention can be applicable to any metal leached by an
aqueous solution. Such metals include the transition metals. The
processes according to the present invention are preferably
employed in the leaching of metals which occur naturally as oxide
and/or sulfide ores. The processes according to the present
invention are most preferably used in the leaching of divalent
metal ores. Such metals include copper, zinc, cobalt and nickel.
The processes according to the present invention are most
preferably used in the leaching of copper.
The aqueous leach solutions treated in the processes according to
the present invention contain a leaching agent which is capable of
leaching the metal from the ore with which they are previously
contacted. The processes according to the present invention are
applicable to leaching operations wherein an aqueous leaching agent
is employed. In certain preferred embodiments of the present
invention the leaching agent comprises sulfuric acid. In those
preferred embodiments of the present invention where the metal
comprises copper, it is further preferred that sulfuric acid be
used as the leaching agent. Other leaching agents which can be used
in processes according to the present invention include, but are
not limited to acids such as hydrochloric acid, nitric acid,
organic acids and combinations thereof, and basic substances such
as ammonia. Essentially, any leaching agent which is
water-miscible, capable of leaching the metal from the ore and
which produces a water-soluble leaching agent-metal compound can be
used.
In the processes according to the present invention, the first
aqueous leach pulp is divided into at least two portions prior to
any solvent extraction, a first clarified leach solution and a
second aqueous leach pulp containing a greater % solids than the
first aqueous leach pulp. Division of the first aqueous leach pulp
can be accomplished via any known process of splitting a leach pulp
into two or more separate streams or volumes. In general, the first
aqueous leach pulp is divided into two portions. The first
clarified leach solution is subjected to solvent extraction prior
to any significant dilution and the second aqueous leach pulp is
taken through a dilution wash circuit to produce a diluted second
clarified leach solution which is then subjected to solvent
extraction. However, the clarified aqueous leach solutions can be
divided into more than two streams, for example, where multiple
circuits are running in parallel. For example, the first clarified
leach solution can be further divided into two portions which
proceed to two solvent extraction plants without any significant
dilution while the second leach pulp undergoes a solid-liquid
separation to give one stream of a second clarified leach solution
which then proceeds to one solvent extraction plant or vice versa.
In a similar manner the first clarified leach solution can be
further divided into two portions which proceed to two separate
solvent extraction plants and the second clarified aqueous leach
solution could also be divided into two separate streams which
proceed to two separate solvent extraction plants. The way the
leach solutions are divided will depend on many factors such as the
metal content of the original leach solution, the design of the
solvent extraction plant, the response of the leach solids to
solid-liquid separation and the total flow of leach solution to be
treated. The important feature of the division of the leach
solution is to take as much of the metal that is leached to the
first solvent extraction plant(s) so as to maximize the
regeneration of the leaching agent. Added division of the leach
solution can occur where volume and capacity require.
The division of the aqueous leach solution in accordance with the
processes of the present invention can be done evenly or such that
one portion contains a greater volume than the other. In certain
preferred embodiments of the present invention, the dividing of the
aqueous leach solution is carried out such that the volume of the
leach solution present in the portion which is subjected to solvent
extraction prior to any significant dilution is greater than the
volume of leach solution present in the portion which is diluted
prior to solvent extraction.
As used herein, the term "significant dilution" refers to the
addition of a measurable amount of water or other aqueous solution
to an aqueous leach solution. Accordingly, significant dilution of
the second aqueous leach pulp refers to the addition of water or
other aqueous solution to the second aqueous leach pulp in an
amount such that the concentration of metal in the first clarified
aqueous leach solution is greater than the concentration of the
metal in the second clarified aqueous leach solution. In preferred
embodiments of the present invention, the concentration of metal in
the first clarified aqueous leach solution is at least 10% greater
than the concentration of the metal in the second clarified aqueous
leach solution. In increasingly more preferred embodiments of the
present invention, the concentration of metal in the first
clarified aqueous leach solution is at least 20% greater, at least
30% greater, at least 40% greater, at least 50% greater, at least
60% greater, at least 70% greater, at least 80% greater, at least
90% greater, at least 100% greater, at least 200% greater, at least
300% greater, at least 400% greater, at least 500% greater, or even
higher than the concentration of the metal in the second clarified
aqueous leach solution. In the most preferred embodiments of the
present invention, the first clarified aqueous leach solution is
subjected to solvent extraction without any dilution. However, it
is to be understood that water or other aqueous solution can be
added to the first clarified aqueous leach solution prior to the
first solvent extraction, but only in such amounts that the
concentration of metal in the first clarified aqueous leach
solution prior to solvent extraction remains greater than the
concentration of the metal in the second clarified aqueous leach
solution. However, as increasing dilution of the first clarified
aqueous leach solution decreases leaching agent recovery, less
dilution is preferred.
Solvent extraction in accordance with the processes of the present
invention can be carried out in any known manner wherein aqueous
leach solution is contacted with an organic phase containing a
metal-specific extraction reagent. Each extraction performed in
accordance with the present invention can be carried out by mixing
the organic phase and the aqueous leach agent and allowing the two
phases to settle. This mixing-settling can be carried out in
multiple series of mixing-settling tanks with countercurrent flow
of the aqueous and non-aqueous phases.
The aqueous phase resulting from a solvent extraction operation is
referred to as a raffinate. In the processes according to the
present invention, the first portion of the aqueous leach solution
is subjected to solvent extraction prior to any significant
dilution and a first aqueous raffinate is obtained. In the
processes according to the present invention, the second portion of
the aqueous leach solution is diluted with an aqueous stream and
then subjected to a separate solvent extraction and a second
aqueous raffinate is obtained. The first raffinate produced in
accordance with the processes of the present invention will
generally have a leaching agent concentration which is greater than
the concentration of leaching agent present in the second
raffinate. In preferred embodiments of the present invention, the
first raffinate will have a leaching agent concentration which is
is at least 10% greater than the concentration of leaching agent
present in the second raffinate. In certain increasingly more
preferred embodiments of the present invention, the first raffinate
will have a leaching agent concentration which is at least 20%
greater, 30% greater, 40% greater, 50% greater, 60% greater, 70%
greater, 80% greater, 90% greater, 100% greater, 200% greater, or
more than the concentration of leaching agent present in the second
raffinate.
In the processes according to the present invention, the second
aqueous leach pulp is diluted prior to being subjected to solvent
extraction. The second aqueous leach pulp is diluted with an
aqueous stream. The aqueous stream for diluting the second aqueous
leach pulp can comprise fresh water introduced into the process, at
least a portion of the aqueous raffinate from another solvent
extraction plant, at least a portion of the second aqueous
raffinate, or a combination thereof. In certain preferred
embodiments of the present invention, the second aqueous leach pulp
is diluted with at least a portion of the second aqueous raffinate.
Where the leaching agent comprises an acid, the second aqueous
raffinate can be at least partly neutralized prior to its use for
diluting the second aqueous leach pulp. Neutralization can be
accomplished via the addition of any basic substance. In those
embodiments wherein the leaching agent comprises sulfuric acid,
lime is preferred for neutralization. Neutralization need not be
complete. A suitable pH range for the partly neutralized second
aqueous raffinate prior to its use for dilution is any pH up to
about 8.
In the processes according to the present invention, a portion of
the second aqueous raffinate may be bled from the circuit to
maintain water balance. Additionally, in certain preferred
embodiments of the present invention, at least a portion of the
first aqueous raffinate is recycled to a leaching operation where
the leaching agent contained therein is employed to leach more
metal from ore. In more preferred embodiments, at least a portion
of the first aqueous raffinate is recycled to the same leaching
operation from which the aqueous leach solution was obtained. In
certain other preferred embodiments of the present invention, at
least a portion of the second aqueous raffinate is recycled to a
leaching operation where the leaching agent contained therein is
employed to leach more metal from ore. In more preferred
embodiments, at least a portion of the second aqueous raffinate is
recycled to the same leaching operation from which the aqueous
leach solution was obtained. In even more preferred embodiments of
the present invention at least a portion of both the first and the
second aqueous raffinates are recycled to a leaching operation
where the leaching agent contained therein is employed to leach
more metal from ore. In still yet more preferred embodiments, at
least a portion of both the first and the second aqueous raffinates
are recycled to the same leaching operation from which the aqueous
leach solution was obtained.
FIG. 1 depicts a process flow diagram of a standard, prior art
agitation leach process for copper followed by solvent extraction.
The leach pulp exiting leaching (LEACH), about 190 cubic
meters/hour, is mixed in counter current decantation (S/L
SEPARATION) with about 630 cubic meters/hour of recycled raffinate
from the dual copper solvent extraction plants (SX 1 & SX 2).
Neutralization of the recycled raffinate is optional. In this way
the copper concentration is diluted from about 24 g/l Cu to about
6.0 g/l Cu prior to being fed to the solvent extraction circuit.
The solvent extraction circuit consists of 2 separate plants or
trains labeled SX 1 and SX 2, respectively, with each plant
treating about 400 cubic meters/hour of aqueous solution flow. The
raffinate exiting the solvent extraction plants are combined and
then a portion of this solution (about 160 cubic meters/hour) is
recycled to the leaching vessel where the acid in the leach
solution is used to dissolve the copper. A second portion of this
solution is recycled to the counter current solid-liquid separation
operation where it is used to wash the leach solution from the
leached solids so as to minimize metal losses to the leached solids
that are eventually disposed to tailings. A small portion of fresh
water may be added to the overall leach/wash system or a small
portion of aqueous solution may be bled from the overall leach/wash
system to maintain a water balance.
FIG. 2 depicts a process flow diagram of a leaching process for
copper followed by solvent extraction according to a preferred
embodiment of the present invention. The aqueous leach pulp exiting
the leach vessel (LEACH), about 190 cubic meters/hour, passes
through an initial solids-liquid separation (S/L SEPARATION). Then
about 120 cubic meters/hour of this solution containing about 26.2
g/l Cu is taken directly to solvent extraction (SX 1) where the
copper is extracted and sulfuric acid is produced. SX 1 will
reasonably produce a raffinate containing about 4 g/l Cu and 35 g/l
acid. This solution is then recycled back to leaching. The aqueous
portion of the leach solution remaining in the leach solution pulp
that has exited the initial solid-liquid separation that does not
proceed to SX 1 (about 70 meters cubed/hour) is taken to a counter
current decantation (CCD) where it is mixed with about 350 cubic
meters/hour of raffinate from SX 2 that has been optionally,
partially neutralized. Then about 400 meters cubed of leach
solution from the CCD circuit containing 4.94 g/l Cu is taken to SX
2 to give a raffinate containing 0.4 g/l Cu and 8 g/l acid. A small
portion of raffinate from SX 2 may be bled from the circuit to
maintain water balance. Additionally about 40 meters cubed/hour of
raffinate from SX 2 is returned to the leaching vessel.
One advantage of the process according to the present invention is
that much more acid is returned to leaching than with the standard
process. For example, by comparing the standard process depicted in
FIG. 1 with the preferred embodiment of the present invention
depicted in FIG. 2, it can be seen that in the standard process,
160 meters cubed/hour of raffinate containing about 9.5 g/l
sulfuric acid is returned to the leaching vessel bringing with it
about 1.52 metric tons of acid per hour. In the process according
to a preferred embodiment of the invention, 120 meters cubed/hour
of raffinate from SX 1 and 40 meters cubed/hour of raffinate from
SX 2 are returned to the leaching vessel bringing a total of about
4.54 tons of acid back to leaching. This represents a savings of
about 3.02 tons of acid/hour or about 72.5 tons of acid/day.
A second advantage of the process according to the present
invention is realized in the neutralization of the recirculating
raffinate if neutralization is needed. For example, by comparing
the standard process depicted in FIG. 1 with the preferred
embodiment of the present invention depicted in FIG. 2, it can be
seen that in the standard process about 630 meters cubed/hour of
solution containing about 9.5 g/l acid is neutralized while in the
process according to a preferred embodiment of the present
invention, about 350 cubic meters/hour of solution containing about
8 g/l acid is neutralized. This results in the need for
significantly less neutralization agent for the practice of this
invention over standard practice.
A third advantage of the process according to the present invention
is that the bleed with the process according to the invention may
in fact contain less metal than the bleed with the normal
configuration. FIG. 1 shows that the bleed for the normal circuit
will contain about 0.5 g/l Cu and 9.5 g/l H.sub.2SO.sub.4 while the
bleed in the process according to the preferred embodiment of the
invention depicted therein will contain only about 0.4 g/l Cu and 8
g/l H.sub.2SO.sub.4. In fact because the feed to SX 1 and SX 2 in
the standard process has about 6.05 g/l Cu while the feed to SX 2
in the preferred embodiment of the inventive process depicted in
FIG. 2 has about 4.94 g/l it is readily apparent to one skilled in
the art that SX 2 in the process according to the invention will
produce a raffinate lower in copper than either SX 1 or SX 2 in the
standard process.
A fourth advantage of the split circuit design pertains to copper
solvent extraction plants where a component of value in the bleed
is recovered, for example cobalt. In most cases the bleed must be
neutralized prior to cobalt recovery. Neutralization with a soluble
base such as caustic or ammonia is very expensive therefore the
lower the acid content of the bleed stream the lower the amount of
base needed for neutralization. Furthermore the use of a solution
of caustic for neutralization adds water to the bleed stream
thereby diluting the valuable cobalt stream. Alternatively
neutralization can take place with lime or limestone which is a
less costly base. In this case a lesser amount of acid in the bleed
stream requires less lime or limestone for neutralization and in
the process a lesser amount of gypsum precipitate is produced.
Gypsum must be removed from the system and all the solution
containing the valuable metal must be recovered. A lesser amount of
gypsum allows the use of smaller equipment for the solid-liquid
separation. When finely divided solids are separated from a liquid
the solids will always contain some of the liquid. In the case
under discussion the lesser amount of gypsum will contain a lower
volume of the neutralized bleed stream which contains the valuable
second component, for example cobalt. Thus the ultimate recovery of
the valuable component in the bleed stream is higher when using the
process according to the invention.
The present invention will now be illustrated in more detail by
reference to the following specific, non-limiting examples.
Comparative Example A & Example B
In Comparative Example A, based on FIG. 1, an aqueous leach
solution is obtained from a leaching operation that produces about
190 cubic meters/hour of leach solution containing 24 g/l Cu and
about 1 g/l sulfuric acid. This leach solution is mixed with a high
volume of recycled and optionally, partially neutralized raffinate,
630 cubic meters/hour containing 0.5 g/l Cu and about 1 g/l
sulfuric acid, to produce an aqueous solution of about 800 cubic
meters/hour containing about 6.05 g/l Cu and about 1 g/l sulfuric
acid. The 800 cubic meters/hour of solution is split into two equal
streams and each stream is then fed to copper solvent extraction
plant. Copper extraction isotherms followed by computer modeling
show that the copper solvent extraction can be expected to produce
a raffinate containing about 0.5 g/l Cu and about 9.5 g/l sulfuric
acid. This represents a copper recovery of 91.7% which is well
within the recovery that can be expected in a commercial copper
solvent extraction plant.
In Comparative Example A, 160 cubic meters of raffinate containing
9.5 g/l sulfuric acid would return to leaching carrying 1.52 metric
tons of acid per hour to leaching.
In Example B, based on FIG. 2, an aqueous leach solution is
obtained from a leaching operation that produces 190 cubic meters
of leach solution containing 26.2 g/l Cu and about 1.0 g/l sulfuric
acid. This leach solution goes directly to a solid-liquid
separation which occurs in a clarifier using decantation. Then
about 120 cubic meters of the clarified leach solution is taken to
a first solvent extraction plant where copper is extracted and
sulfuric acid is produced. Extraction isotherms and computer
modeling show that a raffinate containing about 4 g/l Cu and about
35.2 g/l sulfuric acid can easily be produced by advancing 400
cubic meters of organic flow using a reagent concentration of about
25 to 30 volume % reagent. In this case the acid returned to
leaching in the 120 cubic meters of raffinate is about 4.22 metric
tons/hour.
Also, in Example B, an additional 40 cubic meters of recycled
aqueous solution containing about 8.0 g/l sulfuric acid is returned
to leaching. This brings an additional about 0.32 tons acid/hour to
leaching. Thus the total acid returned to leaching using a process
according to this preferred embodiment of the present invention is
about 4.54 tons per hour.
A simple calculation shows that for this example the acid savings
using the split circuit are about 4.54 metric tons/hour less 1.52
metric tons/hour=about 3.02 metric tons/hour or about 72.5 metric
tons acid/day. Acid costs vary widely from as low as US$ 15/ton to
above US$ 150/ton depending on the location. For low cost-acid, the
savings would be about US$ 1088/day, while for high cost-acid the
savings would be about US$ 10,880/day or higher.
In Comparative Example A, the neutralization of the acid is carried
out on a large portion of the recycled raffinate that does not
proceed directly to leaching, but, rather is used to dilute the
leach solution prior to solvent extraction. About 630 cubic meters
of raffinate flow is taken to neutralization. Additionally, a bleed
of the raffinate prior to neutralization is needed to maintain
water balance in the circuit and can be as high as 20 to 25% or as
low as only a few % of the flow of the leach solution exiting the
leaching vessel. In Comparative Example A, there is a bleed of 10
meters cubed/hour and a raffinate stream to be neutralized of 630
cubic meters/hour. The raffinate contains about 0.5 g/l Cu and
about 9.5 sulfuric acid. When this raffinate is neutralized to a pH
of about 1.8 it will contain about 1 g/l sulfuric acid so the total
acid neutralized is about 5.36 metric tons/hour (630 cubic
meters/hour.times.8.5 kilos acid/cubic meter).
In Example B, the total raffinate taken to neutralization is about
350 meters/cubed hour containing about 8.0 g/l sulfuric acid. Upon
neutralization to a pH of 1.8, the total acid neutralized is about
2.45 metric tons/hour (350 cubic meters/hour.times.7.0 kilos
acid/cubic meter). The savings in neutralization are about 2.91
metric tons acid per hour (5.36 less 2.45). This is a significant
improvement because less acid needs to be neutralized. Less acid
neutralization means that smaller equipment is needed for
neutralization and less base is needed for the neutralization.
Using lime as the neutralization agent in Comparative Example A
produces more than twice the amount of precipitated gypsum as the
neutralization of acid with lime in Example B. Thus the equipment
needed for neutralization and the equipment needed for the
solid-liquid separation after neutralization will be more than
twice in size in Comparative Example A than in Example B.
In Example B, further savings in neutralization are realized
because the leached tailings slurry exiting the solid-liquid
separation must be neutralized to a pH of about 7 to 7.5. In
Comparative Example A, the water contained in the leached tailings
may contain up to about 7.5 g/l sulfuric acid. In Example B, the
water contained in the leached tailings may contain up to about 6.5
g/l sulfuric acid.
In addition the water exiting the CCD circuit with the washed
solids (40 meter cubed per hour) contains 0.8 g/l Cu in the
standard practice while the same amount of water in the practice of
this invention only contains 0.6 g/l Cu. Thus for the exact same
amount of copper ore leached the practice of the present invention
will produce about 192 kilos of copper more per day
(40.times.0.2.times.24).
The bleed from the example under consideration is 10 cubic
meters/hour. In the standard practice this bleed contains about 0.5
g/l Cu while the bleed in the practice of this invention only
contains about 0.4 g/l Cu. Thus the copper lost in the bleed for
the standard practice is about 1 kilo of copper per hour more than
the copper lost in the bleed for the practice of this invention.
For a small bleed the difference in copper lost in the standard
practice compared to the practice of this invention is quite small
but for a plant that has a 20% to 25% bleed the difference in
copper lost can be significant.
In reference to optional neutralization of recycled raffinate it
will be appreciated by those skilled in the art that the level of
neutralization is dependent on the acid consumed by the leached
solids as the leached is solids proceed through the solid-liquid
separation. In some cases considerable acid will be consumed during
the solid-liquid separation and little or no neutralization of the
recycled raffinate will be needed. In other cases only small
amounts of acid may be consumed during solid-liquid separation and
neutralization of the recycled raffinate may be more extensive.
It will be appreciated by those skilled in the art that changes
could be made to the embodiments described above without departing
from the broad inventive concept thereof. It is understood,
therefore, that this invention is not limited to the particular
embodiments disclosed, but it is intended to cover modifications
within the spirit and scope of the present invention as defined by
the appended claims.
* * * * *